Design Of A CCFL (Cold Cathode Fluorescent Lamp) LCD Backlight Controller Chip

A CCFL backlight control chip was designed and implemented in this paper. It is based on the method of pulse width modulation to output the signal in order to control the source outside the chip, and accordingly the lamp. After our design, this chip can provide 2 fully functioned PWM control circuit. The open lamp condition can be detected after lamp period, which ensure the circuit working safely. The lamp dimming can be done through this feedback loop or, by setting the reference DC level of the input of error amplifier. The reference DC level of dimming can be selected as higher level for more brightness or lower level for less brightness. Customer can define the period of soft start signal, and can also decide whether to use the soft start signal. The frequency of PWM wave can also adjusted by engineers through choosing the capacitance.According to the Top-Down IC design method, this paper describes the application background and the design requirements of the chip firstly. Then the structure and the modules of the design, the working mechanism was presented. The main part of this paper provides the design thoughts of every module, including the ON/OFF module, bandgap reference circuit, saw tooth wave generator, bias circuit, PWM module, and protection circuits thoroughly. The detailed circuits and their simulation were also discussed. At the end of this paper, were the layout design and its verification. Now the chip has passed the verification of the simulation and design check.